1. Field of the Invention
The present invention relates to a temperature control apparatus for controlling a heating temperature of a thermal head utilized in a recording apparatus, such as a high-resolution printer.
2. Description of the Related Art
An ink is known that includes fine capsules, such as micro-capsules, filled with heat-sensitive color developing dye or ink for high-resolution printing in a high resolution color printer. A recording sheet consists of a base sheet with a layer of the micro-capsules covering the base sheet. The layer of micro-capsules includes a plurality of types of micro-capsules, each type corresponding to a specific color, which seeps from the micro-capsule onto the recording sheet when the corresponding micro-capsule is heated to a predetermined temperature. The predetermined temperature varies dependent on the type of micro-capsule. Each seeped color is developed and fixed by light of a predetermined wavelength, which also varies dependent on the type of micro-capsule. Therefore, each type of micro-capsule seeps a predetermined color when heated to the predetermined temperature, and the seeped color is developed and fixed on the base sheet of the recording sheet by irradiation with the light of the specific wavelength. Thus, ink or dye of a full-color image, to be recorded on a recording sheet, can be controlled through selective breakage of the micro-capsules as seepage of the dye or ink, which occurs through control of a localized heating and irradiation with a specific wavelength of light.
The recording process utilizing the recording sheet with the layer of the micro-capsules is complicated and time-consuming as the localized heating and light irradiation must be repeatedly executed in order to develop and fix a plurality of colors.
In a printer for producing pixels via a thermal head having one or more heating elements, it is necessary to control a heating temperature of the heating elements through a time controlled application of the electric current. Usually, the heating temperature is measured by a thermistor or another type of temperature sensor. However, due to a small-size of the printer the direct measurement is difficult as the heating elements are extremely small. In this case, the temperature of the heating element cannot be directly measured and is estimated from a resistance of a thermistor disposed adjacent to the heating element within the thermal head. The temperature measured is an ambient temperature of a peripheral area around the heating element.
Due to the temperature not being directly measured, the heating temperature is inaccurate, and the printing quality of the printer, using the thermal head, is thus limited.